1. Field of the Invention
The present invention relates to a high pressure fuel pump control apparatus for an internal combustion engine of a direct injection type, for example. In particular, the invention relates to a technique for facilitating the rising of fuel pressure when an internal combustion engine is started in a state where the pressure of fuel in an accumulator is low (e.g., after the internal combustion engine has been left stopped).
2. Description of the Related Art
Conventionally, in direct injection type internal combustion engines in which fuel is directly supplied by injection to a combustion chamber in each cylinder, the pressure of fuel is raised by pressurizing the fuel to be supplied to each fuel injection valve up to an optimal pressure (a target pressure) for combustion thereof by using a high pressure fuel pump.
In a high pressure fuel pump control apparatus for this kind of internal combustion engine, when the identification of cylinders in the internal combustion engine has been completed, an amount of fuel to be delivered from a high pressure fuel pump necessary to make the fuel pressure in an accumulator detected by a fuel pressure sensor coincide with a target pressure, and a fuel suction valve is closed at predetermined timing in a fuel delivery stroke of the high pressure fuel pump based on the rotational position of the internal combustion engine, whereby the energization timing of a solenoid for the fuel suction valve is controlled so as to deliver a desired amount of fuel from the high pressure fuel pump.
Here, note that the amount of delivery fuel required to make the fuel pressure in the accumulator coincide with the target pressure is calculated according to a proportional integral calculation, etc., based for example on a pressure deviation between a detection value of the fuel pressure detected by the fuel pressure sensor and the target pressure.
The required amount of delivery fuel thus calculated is converted into a corresponding drive timing of the fuel suction valve by using a valve closing drive timing map for the fuel suction valve. The valve closing drive timing map is map data that shows the relation between the valve closing timing of the fuel suction valve and the fuel delivery amount of the high pressure fuel pump, and is stored in advance in a memory in the control apparatus.
A desired amount of fuel is delivered from the high pressure fuel pump by controlling the energization timing of the solenoid in such a manner that the fuel suction valve is closed at the drive timing thus obtained, whereby the fuel pressure in the accumulator is controlled so as to coincide with the target pressure.
However, the fuel pressure in the accumulator is substantially reduced up to the atmospheric pressure at the start-up of the internal combustion engine, so it is necessary to swiftly raise the fuel pressure in the accumulator so as to make it possible to perform a good injection of fuel. Accordingly, in the high pressure fuel pump, it is required to pressure feed as much amount of fuel as possible to the accumulator by driving the fuel suction valve to close at once from a fuel delivery stroke immediately after the beginning of engine starting.
At the start-up of the internal combustion engine, however, a determination as to whether the stroke of the high pressure fuel pump being in synchronization with the rotation of the internal combustion engine is a fuel suction stroke or a fuel delivery stroke can not be made until a time point at which the cylinder identification based on a predetermined pulse signal pattern output from a rotational position sensor (a crank angle sensor or a cam angle sensor) has been completed (i.e., a time point at which the rotational position of the internal combustion engine is fixedly decided). As a result, it is impossible to control the fuel suction valve to close on a fuel delivery stroke before the cylinder identification has been completed. Thus, the solenoid is controlled to be in a non-energized state over a period of time from the beginning of engine starting until the completion of the cylinder identification, and the fuel suction valve continues to be opened, so the pressure feeding of fuel by the high pressure fuel pump is not performed.
Here, note that a low pressure fuel pump arranged at an upstream side of the high pressure fuel pump is of an electrically driven type, and is able to pressure feed fuel at a rated delivery pressure from the beginning of engine starting. Accordingly, the delivery pressure of the low pressure fuel pump acts on the accumulator via the high pressure fuel pump in a period of time from the beginning of engine starting until the completion of the cylinder identification, thereby making it possible to raise the pressure in the accumulator to a rated delivery pressure (e.g., 0.3 MPa) of the low pressure fuel pump. However, this rated delivery pressure is very low as compared with the target pressure (e.g., 7 MPa) in the accumulator in normal operation time, and hence it is difficult to achieve the injection of fuel that is able to obtain a good combustion state.
Accordingly, there has been proposed an apparatus that serves to perform intermittent energization (repetition of on/off) of a solenoid in a period of time from the beginning of engine starting until the completion of the cylinder identification (see, for example, a first patent document (Japanese patent application laid-open No. 2001-182597) and a second patent document (Japanese patent application laid-open No. 2002-309988). According to techniques as described in the first and second patent documents, even in a period of time prior to the cylinder identification in which the rotational position of an internal combustion engine has not yet been detected, a fuel suction valve is driven to close as long as a fuel delivery stroke period that comes after the beginning of engine starting and an on period of a solenoid overlap with each other, whereby fuel is pressure fed from a high pressure fuel pump to an accumulator, thereby facilitating the pressure rising of fuel therein.
In the above-mentioned conventional high pressure fuel pump control apparatuses for an internal combustion engine, there is the following problem. That is, the fuel suction valve is driven to close subject to the condition that the fuel delivery stroke period following the beginning of engine starting and the on period of the solenoid overlap with each other, so it is impossible to achieve the delivery of fuel at a maximum amount that can be output by the high pressure fuel pump as long as the bottom dead center of the fuel delivery stroke (the first or start position of the fuel delivery stroke) and the on period of the solenoid do not overlap with each other superpose by chance.
In addition, the valve closing timing of the fuel suction valve at engine starting becomes a probabilistic or rare operation, so the amount of delivery fuel varies each time the engine is started, and hence the fuel pressure becomes unstable. thus giving rise to a problem that deterioration of the combustion state and exhaust emissions at engine starting might be caused.
For the second-mentioned problem, it is considered to take a countermeasure of setting the on period of the solenoid during the intermittent energization thereof to a long time, but if the on period is set long, the excessive generation of heat of the solenoid becomes aggravated, and a possibility of impairing reliability occurs, so the on period can not in fact be set long.